Hi, thanks for writing to HCM.
This is to inform you that pain should never be felt in the operated bone after a period of 4-5 months from the day of surgery (because this is the maximum time by which the bone should unite) and is considered as abnormal if it occurs.
As per your description, you are getting pain only after 2km of walk. This could be due to
* the nail hitching against the bony cortex
in the medullary canal
* a muscle strain
* too much of nail could be projecting above the surface of upper femur
causing irritation of the muscles
There are many other reasons that are likely to produce pain after nailing of femur.
I suggest you to consult an orthopedic surgeon for proper evaluation and further management.
Hope this helps